Rotary air separators are known as disclosed in U.S. patent application Ser. No. 841,168. In general the apparatus comprises a manifold having an opening through which air is drawn. The manifold is surrounded by a cylindrically shaped screen that rotates past the opening. A mixture of materials, e.g. sawdust, bark, and gravel, is deposited on the screen in the area of the manifold opening. The air flow through the screen and into the manifold has different effects on different materials of the mixture of materials. The fine material (e.g. saw dust), is drawn through the screen (as permitted by the size of the screen openings), and carried by the air flow to a first collection station. The larger-than-screen-size bark is drawn to the screen and carried by the screen past the manifold opening (generally located near the top of the apparatus) to the opposite side of the separator where it is collected at a second collection station. The air flow is established to discriminately draw and hold the lesser mass of the bark. The mass of the gravel is such that it falls from the screen at the infeed side of the apparatus and is collected at a third station.
The problem to which the present invention is directed relates to the air flow. In order to accomplish the separation of the materials, a substantial volume of air is drawn through the manifold. Considering that the overall shape of the apparatus is similar to that of a drum, the air flow is drawn laterally through an opening in the side of the drum, and then redirected axially out the end of the drum. In prior apparatus, as the air is first drawn through the screen and into the manifold opening, distruptive eddy currents are generated. As the air is redirected around corners; i.e., from the side opening to the end, further disruptive eddy currents are generated. These eddy currents significantly negatively effect the system's efficiency.
A further problem with prior rotary air separators is the failure of such devices to generate a consistent air flow across the area of the manifold opening. With one portion of the area of the opening receiving a greater flow of air than another, separation will not be consistent.